On October 20, 1982, 4 days after returning from a rafting trip
down the Omo River in Ethiopia, a Colorado resident noted the onset
of
a low-grade, intermittent fever and myalgias. His symptoms
persisted,
but he did not seek medical attention. However, in early February
1983, a call from another rafter, in whom schistosomiasis had just
been diagnosed, prompted him to visit his physician. Stool
examination revealed eggs of Schistosoma mansoni, and his serum was
positive by the indirect immunofluorescent (IIF) test for
schistosomiasis.

CDC and the Colorado Department of Health were independently
informed of several other possible cases of acute schistosomiasis
mansoni among other participants. Three tour guides had
schistosomiasis mansoni diagnosed by stool examination after the
trip,
and they were symptomatic, with intermittent fever, cough,
lethargy,
and myalgias associated with an absolute eosinophilia ( greater
than
or equal to 600/mm((3))). A fourth guide had developed a 1-cm
diameter, nontender, firm mass on her left buttock but had an
absolute
eosinophila count of 408/mm((3)) and was otherwise asymptomatic.
Her
stool examination revealed eggs of S. mansoni. The mass was not
biopsied but resolved 6 days after treatment with praziquantel.

There were two separate raft trips; the first from September 19
to
October 16, and the second from October 27 to December 4. Both
followed the same route down the Omo River as another trip that led
to
an outbreak of schistosomiasis a year earlier (1). Participants
had
been made aware of the possibility of contracting schistosomiasis
by
the tour organization. Thirty people participated in one or both
trips, and all four U.S.-based river guides were on both trips.
Attempts were made to contact all participants except five staff
from
the Ethiopian office. Four non-U.S. citizens and one U.S. citizen
could not be located. Of 20 participants contacted, 19 had stool
and
serologic examinations performed and completed a questionnaire
concerning exposure; one with a positive IIF test but four negative
stool examinations and a negative rectal biopsy is excluded from
further analysis. Seven (39%) of the 18 participants had S.
mansoni
infection confirmed by stool examinations, and 11 (61%) were
negative
on testing three or more stools and had negative IIF tests.

All seven infected and two uninfected rafters developed an
illness
during or after the raft trips. Six of the seven infected persons
had
onset of a febrile illness, with eosinophilia consistent with acute
schistosomiasis, within 3 weeks after a trip; the seventh was the
guide who developed the soft tissue mass. Quantitative stool
examinations of three infected participants revealed relatively
light
infections with 26, 24, and 18 eggs per gram.

Two persons with schistosomiasis also had confirmed Plasmodium
vivax malaria. Of the two uninfected participants who became ill,
one
developed diarrhea, which resolved with metronidazole during the
trip. The second developed confirmed P. vivax malaria in March
1983.
Finally, stool from one asymptomatic participant had cysts of
Entameba
histolytica.

No specific site of exposure could be identified. Most
participants took few or no precautions other than toweling-off,
despite an awareness of the risk of acquiring schistosomiasis.
However, those who towel-dried most of the time after water
exposure
had a significantly reduced likelihood of infection; eight of 11 of
the noninfected and one of seven of the ill towel-dried after water
exposure during the last third of either trip (p = 0.02).
Reported by J Sisson, MD, Salt Lake City, C Nichols, MPA, Utah
State
Dept of Health; R Hopkins, MD, State Epidemiologist, Colorado State
Dept of Health; Div of Field Svcs, Epidemiology Program Office,
Helminthic Diseases Br, Div of Parasitic Diseases, Center for
Infectious Diseases, CDC.

Editorial Note

Editorial Note: This outbreak of acute schistosomiasis mansoni
resembles an outbreak that occurred in 1981 (1). The unusual
presentation of schistosomiasis as a subcutaneous mass has been
previously described with S. japonicum, S. mansoni, and S.
hematobium. While the present case was not parasitologically
confirmed, the rapid resolution of the mass after praziquantel
therapy
suggests that it was schistosomal.

With multiple potential sites of exposure along the route, the
exact mode and site of exposure could not be distinguished. For
such
an activity, exposure would be difficult to avoid, and such
measures
as chemically treating or heating water before bathing would not
always be possible. Nevertheless, epidemiologic data gathered on
these trips imply that towel-drying after exposure to infested
water
can markedly reduce the risk of infection supporting the
recommendations that this is a useful protective measure (2).

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